Such pressure measuring arrangements are used if a pressure to be measured cannot be delivered directly to the pressure measuring cell. This is the case for instance whenever the pressure measuring cell is very vulnerable to chemical and/or mechanical stresses, as is the case for instance with piezoresistive pressure measuring cells that for instance have measuring membranes comprising or having vulnerable semiconductor components, or if a difference between two pressures that act at different locations is to be detected with a measuring cell embodied as a differential-pressure measuring cell. Such pressure measuring arrangements are also used if a ceramic pressure measuring cell is to be used and if, for instance for hygienic reasons, a flush closure off from the process at the front is desired. These pressure measuring arrangements must be filled, once their manufacture is concluded, with a fluid that transmits the pressure corresponding to the pressure to be measured. To that end, the measuring arrangement is evacuated, for instance, and placed in a bath with the fluid and flooded. The fill openings are then closed, and the measuring arrangement can be connected to a site where it will be used.
Since the filling is comparatively complicated and requires special operating media, a measuring arrangement once completed is as a rule no longer changed.
For the sake of great flexibility with a view to measuring arrangements that can be furnished quickly, examples being various possible combinations of different pressure measuring cells with different pressure measurement recorders, or different oil supplies or pressure lines of different lengths, without having to keep all possible variants of pressure measuring arrangements on hand in adequate numbers, it is therefore desirable for such a pressure measuring arrangement to be embodied in modular fashion and then put together and filled as needed.
U.S Pat. No. 4,833,922 describes a differential-pressure measuring cell of modular construction, having: a pressure measuring cell, to which a pressure corresponding to a pressure to be measured is delivered via a fluid-filled pressure tube; at least one pressure recording unit, on which in operation a pressure to be measured acts, and which makes a pressure corresponding to the pressure to be measured available via a fluid-filled pressure line; and a connection between the pressure tube and the pressure line.
The differential-pressure measuring cell is very compactly designed. To that end, the pressure measuring cell is disposed directly in the pressure recording unit, and the pressure tubes are introduced into bores of the pressure recorder that form pressure lines. Frustoconical sealing elements are provided, which annularly surround the pressure tubes and are introduced into recesses of the same shape in the pressure recorder. A fastening is provided that presses the sealing elements inward into the recesses of the same shape. The fastening surrounds the pressure tubes annularly and is screwed onto the pressure recorded, for instance by means of tension bolts.
Such a compact design is not always usable. For instance, space conditions at the usage site, high temperatures acting on the pressure recorder, or pressure measuring cells that require a special mode of installation, for instance in a manner that is as free from fastening as possible, necessitate a spatial separation of the pressure measuring cell and the pressure recorder.